Method and system for robust MAC signaling

ABSTRACT

A method for indicating and interpreting robust MAC signaling, the indicating method having the steps of: checking whether a MAC-PDU contains control information; and if yes, providing an indication to use a robust configuration for a HARQ feedback transmission, and the interpreting method having the steps of: receiving a MAC-PDU; checking whether an indication for robust HARQ feedback transmission is provided; and if yes, utilizing robust HARQ feedback transmission.

FIELD OF THE DISCLOSURE

The present disclosure relates to the long term evolution (LTE) of ThirdGeneration Partnership Project (3GPP), and in particular to HARQfeedback transmission from user equipment (UE) in the LTEinfrastructure.

BACKGROUND

In the long term evolution infrastructure, one proposal being studied isthe use of control information in the MAC-PDU header. This can be used,for example, with discontinuous reception (DRX) of user equipment in anLTE_Active state. The 3GPP TSG-RAN Working Group 2 proposal R2-063081proposes that regular DRX configuration be signaled by radio resourcecontrol (RRC) protocol and that temporary DRX configuration is signaledby Medium Access Control (MAC) signaling.

A problem with the sending of control information in the MAC-PDU headeris due to HARQ feedback errors. In particular, when the enhanced Node B(eNB) misinterprets a NACK as an ACK for the downlink MAC data. Inparticular, with in band DRX parameters which configure a shorter DRXvalue than that of the already assigned DRX, the UE would misssubsequent downlink MAC data as sent from the eNB.

BRIEF DESCRIPTION OF THE DRAWINGS

The present application will be better understood with reference to thedrawings, in which:

FIG. 1 is a block diagram showing a long term evolution user planeprotocol stack;

FIG. 2 is a block diagram showing a long term evolution control planeprotocol architecture;

FIG. 3 a is a flow chart showing a method to activate, deactivate andreconfigure DRX period using a MAC-PDU header from the eNB side;

FIG. 3 b is a flow chart showing a method to acknowledge the activation,deactivation or reconfiguration of the DRX period from the UE side;

FIG. 4 a is a flow chart showing a method on an eNB to indicate robustHARQ feedback transmission should be used by using a reserved DLSCCH;

FIG. 4 b is a flow chart showing a method on a UE to utilize robust HARQfeedback transmission using a reserved DLSCCH;

FIG. 5 a is a flow chart showing a method on an eNB to indicate robustHARQ feedback transmission should be used by using a one bit indicationon DLSCCH;

FIG. 5 b is a flow chart showing a method on a UE to utilize robust HARQfeedback transmission using a one-bit indication on DLSCCH;

FIG. 6 a is a flow chart showing a method on an eNB to indicate robustHARQ feedback transmission should be used by using two RNTIs;

FIG. 6 b is a flow chart showing a method on a UE to utilize robust HARQfeedback transmission using two RNTIs;

FIG. 7 a is a flow chart showing a method on an eNB to indicate howrepetition for HARQ feedback transmission should be used; and

FIG. 7 b is a flow chart showing a method on a UE to utilize repetitionfor HARQ feedback transmission.

DETAILED DESCRIPTION OF THE DRAWINGS

The present disclosure provides various methods and systems foraddressing the deficiencies and the prior art regarding HARQ feedbacktransmission.

In particular, the present system and method provides for a more robustand reliable HARQ feedback transmission in the case of controlinformation being sent in the MAC-PDU. The method and system of thepresent disclosure includes signaling by the RRC of a configuration forUE HARQ feedback transmission for a normal MAC-PDU and a robustconfiguration for UE HARQ feedback transmission for a MAC-PDU whichcontains control information. The method and system further provide forthe eNB indicating, when a MAC-PDU is transmitted, if the UE should usestandard or robust configuration for HARQ feedback transmission.

Four potential methods for indication between the eNB and the UE areoutlined. These include the use of a reserved downlink shared controlchannel where the sending of a MAC-PDU is signaled on a reserved DLSCCH,specifically if there is control information in the MAC-PDU being senton the downlink shared data channel and otherwise the sending of theMAC-PDU is signaled on a different DLSCCH.

A further indication method is the use of a one-bit indication on theDLSCCH. Specifically, the one-bit indication could be set to indicatewhether the UE should use standard or robust configuration for HARQfeedback transmission when it sends an ACK or a NACK after receiving theassociated MAC-PDU on the downlink shared channel associated with theDLSCCH.

A third indication method is the use of two radio network terminalidentifiers (RNTIs). The UE is configured by the RRC with two RNTIs. OneRNTI is used for MAC-PDUs with control information in the header tosignify robust HARQ and the second RNTI is used for MAC-PDUs withoutcontrol information in the header to signify normal HARQ. Thus the UEknows whether to use a more robust HARQ feedback transmission or not.

A fourth method for indication is to use a repetition field in theMAC-PDU header itself. The repetition field would be used to indicatethat the HARQ feedback transmission should occur several times, wherethe number times that the HARQ feedback transmission should be sent isspecified in the repetition field. The eNB could then monitor thereceived acknowledgements in order to determine the reliability of theUE signaling, e.g. whether more ACKs were received than NACKs or DTXs.

The present disclosure therefore provides a method for indicating robustMedium Access Control (MAC) signaling comprising the steps of: checkingwhether a MAC protocol data unit (MAC-PDU) contains control information;and if yes, providing an indication to use a robust configuration for ahybrid automatic repeat request (HARQ) feedback transmission.

The present disclosure further provides a method for interpreting anindication of robust Medium Access Control (MAC) signaling comprisingthe steps of: receiving a MAC protocol data unit (MAC-PDU); checkingwhether an indication for robust hybrid automatic repeat request (HARQ)feedback transmission is provided; and if yes, utilizing robust hybridautomatic repeat request (HARQ) feedback transmission.

The present disclosure further provides an enhanced Node B (eNB) adaptedto indicate robust Medium Access Control (MAC) signaling, characterizedby: means for checking whether a MAC protocol data unit (MAC-PDU)contains control information; and means for providing an indication touse a robust configuration for a hybrid automatic repeat request (HARQ)feedback transmission.

The present disclosure still further provides a User Equipment (UE)adapted to interpret an indication of robust Medium Access Control (MAC)signaling, characterized by: means for receiving a MAC protocol dataunit (MAC-PDU); means for checking whether an indication for robusthybrid automatic repeat request (HARQ) feedback transmission isprovided; and means for utilizing robust hybrid automatic repeat request(HARQ) feedback transmission.

Reference is now made to the drawings. FIG. 1 shows a block diagramillustrating the long-term evolution (LTE) user plane protocol stack.

A UE 110 communicates with both an evolved Node B (eNB) 120 and anaccess gateway (aGW) 130.

Various layers are illustrated in the protocol stack. The packet dataconvergence protocol (PDCP) layer 140 is illustrated both on the UE 110and on aGW 130. The PDCP layer 140 performs internet protocol (IP)header compression and decompression, encryption of user data, transferof user data and maintenance of sequence numbers (SN) for radio bearers.

Below the PDCP layer 140 is the radio link control protocol layer 142,which communicates with the radio link control protocol layer 142 on theeNB 120. As will be appreciated, communication occurs through thephysical layer in protocol stacks such as those illustrated in FIGS. 1and 2. However, RLC-PDUs from the RLC layer 142 of the UE areinterpreted by the RLC layer 142 on the eNB 120.

Below RLC layer 142 is the medium access control (MAC) datacommunication protocol layer 146. As will be appreciated by thoseskilled in the art, the RLC and MAC protocols form the data linksublayers of the LTE radio interface and reside on the eNB in LTE anduser equipment.

The layer 1 (L1) LTE (physical layer 148) is below the RLC/MAC layers144 and 146. This layer is the physical layer for communications.

Referring to FIG. 2, FIG. 2 illustrates the LTE control plane protocolarchitecture. Similar reference numerals to those used in FIG. 1 will beused in FIG. 2. Specifically, UE 110 communicates with eNB 120 and aGW130. Further, physical layer 148, MAC layer 146, RLC layer 142 and PDCPlayer 140 exist within FIG. 2.

FIG. 2 also shows the non-access stratum (NAS) layer 210. As will beappreciated, NAS layer 210 could include mobility management and sessionmanagement.

The radio resource control protocol layer (RRC) 220, is the part of theprotocol stack that is responsible for the assignment, configuration andrelease of radio resources between the UE and the E-UTRAN (Evolveduniversal terrestrial radio access network). The basic functionalitiesof RRC protocol for LTE is described in 3GPP TR25.813.

As will be appreciated by those skilled in the art, in UMTS, automaticrepeat request (ARQ) functionality is carried out within the RLC layerwhich resides in the radio network controller (RNC). Long Term Evolution(LTE) moves the ARQ functionality from the RNC to eNB where a tighterinteraction may exist between the ARQ and the HARQ (within the MAClayer, also located in the eNB).

Various issues regarding DRX in an LTE-ACTIVE state are consideredherein.

DRX Signaling Procedure

Very efficient signaling procedures for activating and de-activating DRXand specifying the duration of DRX periods are required in order tosupport a large population of UEs in a cell that are utilizing DRX in anLTE_ACTIVE state.

As will be appreciated by those skilled in the art, if the evolved NodeB (eNB) transmits data to the UE during its receiver off period due to aDRX operation, the UE cannot receive the data. Therefore, special effortis required to ensure the UE and the eNB are synchronized regarding whenDRX is activated and deactivated.

The indication between the UE and the eNB can be explicit signaling bythe radio resource control (RRC) or layer 1/layer 2 (L1/L2) signaling.As will be appreciated, however, explicit signaling may not be asefficient as desired.

A more efficient solution is to include an optional field in the MACheader of a MAC-PDU (MAC Protocol Data Unit) to indicate DRX activationand deactivation. The field preferably indicates the DRX value andtiming margin for activation and deactivation. A value of zero, forexample, could mean DRX deactivation in the DRX value field in apreferred embodiment. Conversely, if data that is to be transmitted inthe next MAC-PDU is the last one in the buffer for the UE, the eNB mayextend the MAC header field to include a DRX length initial value. Forexample, this could be 320 milliseconds.

The timing margin is explained below, and is utilized to reduce theconsequences of a NACK to ACK or ACK to NACK misinterpretation, for thereception status of the MAC-PDU between the UE and the eNB.

Several different methods for signaling the DRX period within theMAC-PDU header can be envisaged. For example, three bits may be added tothe MAC header to indicate eight values of the DRX period. Thus, ratherthan a specific time value being sent, a bit value from 000 to 111 couldindicate one of eight discrete values.

In an alternative, a smaller field in the MAC header could be used (forexample two bits) to indicate increment or decrement. The RRC couldindicate default values, and if the MAC header indicates increment ordecrement then the UE could change to the pre-specified value, accordingto the received indication. Similarly, the RRC could define the mappingbetween the actual DRX value and the value contained in the smallerfield.

Once the UE receives the DRX value, it acknowledges it to the eNB bytransmitting HARQ ACK and starts the DRX at the appropriate system frameconsidering propagation delay and processing delay at the eNB. When theeNB receives the ACK from the UE, it also starts the DRX at theappropriate system frame time. As will be appreciated, the eNB does notturn off its transceiver, but simply knows not to transmit messages tothe individual UE.

During the awake cycle of a DRX period, if new data has arrived at theeNB for transmission, the eNB can send a MAC-PDU with a header extensionset to DRX deactivation or a shorter DRX length depending on the amountof data in the buffer or the quality of service requirements. The UEreconfigures the DRX accordingly and acknowledges the MAC-PDU. When theeNB receives the ACK, it reconfigures the DRX. As indicated above, thedeactivation could be accomplished by merely setting the length value tozero.

Reference is now made to FIG. 3 a and 3 b. FIG. 3 a shows an exemplarymethod for controlling DRX activation in the LTE_ACTIVE state. Theprocess starts at step 300 and proceeds to step 310 in which data istransmitted to the UE. As will be appreciated by those skilled in theart, data transmission in the LTE_ACTIVE state utilizes the MAC-PDU atthe data link layer to transmit the data.

The process next proceeds to step 312 in which a check is made to seewhether the buffer of data to be sent to the UE will be empty after thenext transmit. If no, the process proceeds back to step 310 in whichdata is transmitted to the UE. Alternatively, if the buffer will beempty after the next transmit and the data arrival rate is lower than athreshold value, the process proceeds to step 314.

In step 314, the eNB sets DRX activation in the MAC-PDU header. Asindicated above, this includes a DRX activation value indicating thelength of the DRX period. In another embodiment the eNB may simplyindicate an increase in the DRX interval. The UE reconfigures theexisting DRX interval to a predetermined reduced interval. Thepredetermined interval may be either known to both eNB and UE orpre-signaled to the UE from the eNB via explicit signaling; either bysystem broadcast or RRC signaling.

The process then proceeds to step 316 in which the data including themodified MAC-PDU header is sent to the UE.

Reference is now made to FIG. 3 b. In step 318, the UE receives the dataand sees that DRX activation is specified in the MAC-PDU header. Theprocess proceeds to step 320 in which the UE sends an acknowledgement(ACK) to the eNB and starts the DRX at the appropriate system frameconsidering propagation delay and processing delay at the eNB.

In step 330 of FIG. 3 a, the eNB receives the ACK from the UE and startsthe DRX at the next system frame.

As will be appreciated, the DRX can continue until various events occurwhich may require the DRX to be adjusted. One event is the reception ofdata from the aGW by the eNB for the UE. Depending on the amount of datareceived, the DRX can either be deactivated or the period of the DRX canbe reduced. Other events that may require the adjustment of the DRXinclude a change of signal power level between the eNB and the UE orpossibly a gradual increase in the DRX cycle due to continued datainactivity, among others. These other events are discussed in moredetail below.

In step 332 the eNB checks to see whether the DRX needs to be adjusted.As indicated above, this could be the situation where data is receivedto be sent to the UE. Here the DRX can either be deactivated or theperiod adjusted.

From step 332, if the DRX does not need to be adjusted, the processproceeds back to step 332 and continues to check whether or not the DRXneeds to be adjusted.

Once the process in step 332 finds that the DRX does need to beadjusted, the process proceeds to step 334 in which it adjusts the DRX.This could be deactivating the DRX by transmitting a zero value for theDRX or a shorter DRX or a longer DRX as required.

The MAC-PDU with the modified header is sent to the UE in step 336. TheMAC-PDU in step 336 could also include any data that has been receivedby the eNB that needs to be transmitted to the UE.

Referring to FIG. 3 b, the process then proceeds to step 318 in whichthe MAC-PDU with modified header is received at the UE. The UErecognizes the DRX period is to be adjusted and in step 320 it sends anacknowledgement to the eNB and it adjusts its DRX period at theappropriate system frame considering propagation delay and processingdelay as at the eNB.

Referring to FIG. 3 a, in step 342 the eNB receives the ACK and startsthe modified DRX period at the appropriate system frame. The processthen proceeds back to step 332 to see whether the DRX needs to beadjusted again.

As will be appreciated by those skilled in the art, one issue with theabove occurs in the case of a misinterpretation of an ACK or a NACK.Specifically, the transmitter's hybrid automatic repeat request (HARQ)entity, which is a variation of the ARQ error control method, does notalways properly demodulate an ACK or a NACK possibly due to poor channelconditions. Thus, in some situations, one can be interpreted as theother. By having the DRX activation and deactivation occur in theMAC-PDU header, an ACK to NACK or NACK to ACK misinterpretation needs tobe handled as misinterpretation of control information signaled betweenan eNB and a UE can lead to loss of data or possibly radio connection.

A possible solution to the above is the introduction of timer thresholdvalues before activating or deactivating DRX.

When the UE NACKs a MAC-PDU that has DRX header information, the UE isunaware that it should adjust the DRX period. It will expect aretransmission from the eNB. If a NACK to ACK misinterpretation occurs,the eNB receives an ACK and it will not send a retransmission and willchange the DRX period as originally signaled. The UE waits for a time toreceive the retransmission. This time should be limited by an upperthreshold (TH-A) considering possible NACK to ACK misinterpretations. Ifthe UE does not receive a retransmission, it should maintain its currentDRX status. The eNB will expect an exchange of information with the UEat the next DRX period. If the UE does not respond, the eNB shouldrevert to the previous DRX period and attempt to “synchronize” with theUE.

Even in the case where a UE ACKs a MAC-PDU, the UE needs to wait forretransmission due to possible ACK to NACK misinterpretation or possibleACK to DTX misinterpretation by the eNB. This waiting time should belimited by an upper threshold (TH-B).

If the UE is missing data as indicated on the L1/L2 signaling channel,assuming the eNB will retransmit at the next earliest opportunity, theUE needs to check the L1/L2 signaling channel within a certain duration(TH-C).

Based on the various threshold parameters above, the minimum time beforeDRX activation should therefore be greater than (max(TH-A, TH-B)+TH-C).This threshold value can be signaled either by system broadcast or RRCsignaling.

Various scenarios are considered herein:

DRX Activation and ACK to NACK Errors:

For an ACK to NACK misinterpretation or an ACK to a discontinuoustransmit (DTX) misinterpretation (i.e. the channel conditions are sopoor that the ACK appears as noise to the receiver), the followingoccurs. The UE receives the DRX activation in the header of the MAC-PDUand sends an ACK to the eNB. The eNB receives the ACK but misinterpretsit as a NACK or a DTX misinterpretation. This results in the UEactivating the DRX before the eNB, which may result in the UE missingthe retransmission of the MAC-PDU from the eNB.

In the situations indicated above, an ACK to NACK or DTXmisinterpretation can be solved by the UE waiting for the timing marginbefore activation of DRX. The margin can be based on the normal timethat it takes a retransmission to occur and weighted by the averagenumber of HARQ retransmissions to the UE that may be experienced. Whenthe UE acknowledges the retransmission and starts the DRX at theappropriate system frame considering propagation delay and eNBprocessing time assuming that two consecutive misinterpretations arevery unlikely.

DRX Activation and NACK to ACK Errors:

Similarly, if the UE sends a NACK for a MAC-PDU, this could bemisinterpreted as an ACK by the eNB. In the case of DRX activation, theeNB activates the DRX before the UE. If the eNB maintains the CQImonitoring for the UE for a short period of time after activating DRX,it will detect that the UE has not activated the DRX indicated bychecking the frequency of CQI report and it can re-signal the DRXactivation by L1/L2 control signaling. If the eNB releases the CQIresource just after activating DRX and assigns it to another UE, CQIreports from the two UE may collide. The eNB could use Time DivisionMultiplexing or Code Division Multiplexing to avoid the collision.

One solution is, in the HARQ, the receiver sends a channel qualityindicator (CQI). In continuous reception, the channel quality indicatoris repeated every 100 milliseconds, for example. Based on this CQIreport, the transmitter decides and indicates a coding rate, modulationscheme, and Transport Block size. During active DRX, the eNB may expecta CQI, for example, every second. If the eNB gets this CQI at adifferent rate (for example 300 milliseconds) it knows that the UE isnot in DRX and a correction can occur.

In the case that the RLC is operating in acknowledged mode (AM), when aNACK to ACK misinterpretation occurs, recovery for DRX synchronizationbetween the eNB and the UE is established via the normal RLCretransmission mechanism. This is because the RLC layer in thetransmitter will determine that the PDU is lost and therefore instigatenormal ARQ recovery by resending the original data not received.

In the case that the RLC is operating in unacknowledged mode (UM mode),no recovery mechanism exists.

Thus assuming that the CQI (channel quality indicator) reporting will bealigned to the DRX length, the eNB will know if DRX activation iscompleted in the UE by checking the frequency of CQI reporting. If notcompleted, the eNB may use L1/L2 signaling or send only a MAC-PDU headerto correct the DRX activation or reconfiguration.

Another recovery method can triggered when the eNB receives a TimingAdvance (TA) Request message from a UE that should be in DRX. When theUE returns power to its transceiver and, hence, emerges from the DRXstate, it will often need to send control (e.g. measurement reports) andother data messages the eNB. It is important that the UE have the properTA before sending these messages so that the UE messages do notpartially overlap with messages from other UEs as they arrive at theeNB. Hence, after a DRX cycle the UE will often send a TA Request on arandom access channel so that it can get the proper TA from the eNB. Ifthe TA request arrives at a point when the UE should be in DRX, the eNBwill know that the UE did not receive the last DRX activation ormodification properly. The eNB can then revert to the prior DRX periodfor that UE and recover DRX-period synchronization.

DRX Deactivation and ACK to NACK Errors:

In the case of DRX deactivation or DRX length reconfiguration, an ACK toNACK or DTX misinterpretation leads to the UE deactivating the DRXbefore the eNB, which may require no special handling if the UEacknowledges the normal retransmission from the eNB and the eNBsuccessfully received the ACK.

DRX Deactivation and NACK to ACK Errors:

In the case of DRX deactivation or DRX length reconfiguration, a NACK toACK misinterpretation results in the eNB deactivating the DRX before theUE, which may result in the UE missing the new data transmissions. Thepossible solution to this is that the eNB indicates DRX deactivation ona MAC-PDU header extension of subsequent MAC-PDUs. Assumptions are thatconsecutive misinterpretations are very unlikely and that no DRXreconfiguration is needed when only one MAC-PDU is needed to transmitthe new data which has arrived at the eNB.

Robust Mac Signaling

The above therefore illustrates some deficiencies of ACK to NACK andNACK to ACK misinterpretations occurring. As will be appreciated bythose skilled in the art, standardized methods exist to reduce anACK/NACK detection error probability for UTRA (UMTS Terrestrial RadioAccess). For example, more transmission power can be applied forACK/NACK messages, repetition of ACK/NACK messages or the use of apreamble and post amble are described in 3GPP TS25.213, section 4.2.2.1and 3GPP TS25.214 section 6A.1. In these solutions, the UE increases thetransmission power of an ACK or a NACK by the amount configured by theRRC, repeats the ACK or NACK N times, where N is usually between 2 and4, as specified by the RRC, or places a preamble before the ACK or NACKand a post amble after the ACK or NACK. Currently, such configurationsare applied to all MAC-PDUs carried on a radio bearer once activated.Such methods may also be applicable to LTE.

The above, however, may not be optimal for the case of MAC DRX signalingor any other signaling in which a configuration message is sent in theMAC-PDU header. As will be appreciated, a configuration message caninclude both the DRX message described above, and other messages, and isnot meant to be limited in the present disclosure. Preferably, a morerobust configuration of UE HARQ feedback transmission is applied when aMAC-PDU contains important control information. In this preferredembodiment, the standard configuration of UE HARQ feedback transmissionis applied when a MAC-PDU contains only data or control information notrequiring robust feedback signaling. By applying a more robustconfiguration for UE HARQ feedback only when the MAC-PDU containscontrol information, this provides for a more efficient usage of radioresources.

In operation, the proposed solution comprises the RRC signaling aconfiguration for UE HARQ feedback transmission for a normal MAC-PDU anda robust configuration for UE HARQ feedback transmission for a MAC-PDUwhich contains important control information in its header, which issubsequently identified to require robust feedback transmission. The RRCsignaling occurs when a radio bearer is configured or reconfigured.Alternatively the RRC signaling can be configured as common for allradio bearers and can be signaled at RRC connection set up or as adefault configuration via system broadcast information. Subsequently,when a MAC-PDU is transmitted, the eNB indicates if the UE should usethe standard or the robust configuration for the HARQ feedbacktransmission. As will be appreciated by those skilled in the art, any ofthe known robust HARQ feedback techniques could be used. Specifically,the transmission power could be increased, the ACK or NACK could berepeated a specified number of times or a preamble or post amble couldbe added to the ACK or NACK.

The indication between the eNB and the UE to indicate whether a robustconfiguration for HARQ feedback transmission should be utilized couldinvolve various techniques. Four are described below.

Use of a Reserved Downlink Shared Control Channel (DLSCCH)

Reference is now made to FIGS. 4 a and 4 b.

As will be appreciated by those skilled in the art, a downlink sharedcontrol channel (DLSCCH) is used to indicate the transmission of aMAC-PDU on an associated DL-SCH. A UE will typically monitor severaldownlink shared control channels. A first proposed means for anindication between the eNB and the UE is the utilization of a reservedDLSCCH to indicate transmission of a MAC-PDU including controlinformation to the UE. When the radio bearer is configured initially,the UE is informed by the RRC of which DLSCCHs are reserved for thatpurpose. The RRC will provide the UE with information about the type offeedback to use. After the UE receives the MAC-PDU on the downlinkshared channels associated with the reserved DLSCCH, the UE will thenapply the configuration for HARQ feedback transmission when, dependingon the results of the decoding process, it sends an ACK or NACK.

Referring to FIG. 4 a, an eNB starts the process at step 410 andproceeds to step 412 in which the eNB checks whether control informationis being sent in the MAC-PDU header.

If yes, the eNB proceeds to step 414 in which it uses the reservedDLSCCH, to indicate the impending transmission of a MAC-PDU for the UE.Otherwise, the process proceeds to step 416 in which it uses anon-reserved DLSCCH, to indicate the impending transmission of a MAC-PDUfor the UE.

The eNB then transmits the MAC-PDU in step 420 utilizing the downlinkshared channel associated with the DLSCCH assigned in steps 416 or 414.

The process then ends at step 430.

Referring to FIG. 4 b, on the UE the process starts at step 450 andproceeds to step 452, in which a MAC-PDU is received. The process thenproceeds to step 454 in which a check is done to see whether or not theindication of MAC-PDU transmission was received on a reserved DLSCCH. Ifyes, the process proceeds to step 456 in which a robust ACK or NACK isused. Otherwise, the process proceeds to step 460 in which a normal ACKor NACK is used.

The process then ends at step 470.

As will be appreciated, in the existing implementation of HSDPA (HighSpeed Downlink Packet Access) within UMTS, the UE is required to listento a set of up to four DLSCCHs for an indication of a data transmissionon a DL-SCH(HS-PDSCH).

The above establishes that one of the identified DLSCCHs is dedicatedfor the transmission of a MAC-PDU which also contains specific controldata. In other words, a special action is required when receiving thisPDU on the DL-SCH compared to receiving one indicated on another DLSCCH.

In one embodiment, a repetition scheme for the HARQ feedback process forthe reception of the PDU is applied, thereby providing more reliablefeedback detection by the network. This then gives the network a greaterreliability that the UE has implemented the new configuration as sentvia the control information in the MAC header and that the UE can alsoact on this indicated control information accordingly.

While repetition of the HARQ feedback is one specific behavior that maybe interpreted from the use of the special DLSCCH, it is also possiblefor several other specific behaviors to be identified.

Specifically, it will be recognized by those skilled in the art that theMAC-PDU could have a different format when compared to a MAC-PDU notindicated on the reserved DLSCCH control channel in order to incorporateadditional header information e.g. DRX period. Thus, the format of thebits will be interpreted in a specific manner different to the MAC-PDUheader indicated on another DLSCCH control channel. This ensures correctdecoding and interpretation of this MAC-PDU signaled using this reservedDLSCCH. Also, a further consideration is that when using the alternateMAC-PDU format, data may or may not be included.

As an extension to the above, a reserved DLSCCH could be used as adefault indication channel for UEs that are accessing the network in anunsynchronized manner. This would then enable special configuredsignaling to be incorporated into the MAC-PDU which may differ fromother regularly used MAC-PDU formats. This could include an indicationof temporary network identifiers or a change of existing identifiers ifnecessary within the MAC header.

Use of One Bit Indication on DLSCCH

As an alternative to using a reserved downlink shared control channel, asingle bit could be defined in the information signaled on the DLSCCH.The bit is used to indicate if the UE should use standard or a robustconfiguration for HARQ feedback transmission when it sends an ACK or aNACK after receiving the MAC-PDU on the downlink shared channelassociated with the DLSCCH. When the eNB sends a MAC-PDU with controlinformation in the header, the eNB sets the bit.

As will be appreciated by those skilled in the art, the bit could beplaced anywhere. For example, the bit could be placed next to the HARQprocess indicator field. However, this is not meant to limit the bitplacement, and as indicated above, the bit could be placed anywhere inthe information signaled on the DLSCCH.

Reference is now made to FIGS. 5 a and 5 b. FIG. 5 a illustrates a flowdiagram from the eNB perspective. Specifically, the process starts atstep 510 and proceeds to step 512 in which the eNB checks whethercontrol information is to be sent in the MAC-PDU header. If yes, theprocess to step 514 in which the bit in the DLSCCH is set to indicaterobust feedback.

If, from step 512, the eNB determines that no control information is tobe sent in the MAC-PDU header, the process proceeds to step 516 in whichthe bit in the DLSCCH is set to indicate normal feedback.

The process then proceeds from step 514 or step 516 to step 520 in whichthe eNB transmits the MAC-PDU and signals on the DLSCCH.

The process then ends at 530.

Reference is now made to FIG. 5 b which illustrates the process from theUE perspective.

The process starts at step 550 and proceeds to step 552 in which the UEreceives the MAC-PDU.

The process then proceeds to step 554 in which the UE verifies theindication received on the DLSCCH to see whether the bit is set toindicate the use of robust or normal feedback. If the bit is set torobust feedback, the proceeds to step 556 in which a robust ACK or NACKis used depending on the result of the decoding process. Otherwise, theprocess proceeds to step 560 in which a normal ACK or NACK is useddepending on the result of the decoding process.

The process then proceeds to step 570 and ends.

In the case where there is a one bit indicator to indicate therequirement of special handling for certain MAC-PDUs, no suchrestriction would necessarily be imposed for successive transmissions.However, it may be appreciated that if a control MAC-PDU changes someconfigurations and/or requires some special behavior for HARQ feedbacksignaling, it may not be desirable to transmit in successive TTIs in anycase, due to allowing time for the UE to reconfigure itself according tothe control information received.

Use of Two Radio Network Temporary Identifiers (RNTI)

A further indication between the eNB and UE that more robustconfiguration is required for HARQ feedback transmissions could be theuse of two RNTIs allocated to the UE by the eNB. A first RNTI is usedwhen MAC-PDUs without control information are transmitted to the UE andthe other is used when MAC-PDUs with control information are transmittedto the UE. The UE recognizes which RNTI is used and applies a differentconfiguration for transmitting HARQ feedback, depending on the RNTIindicated. The eNB signals the two sets of RNTI and configuration ofHARQ feedback transmission by using the RRC.

As will be appreciated by those skilled in the art, any two RNTIs can beused. In one embodiment, an RNTI and its logical complement could beused. Thus, instead of two RNTIs being sent to the UE, one could bechosen and signaled. The processor on the UE would then be able todetermine the complement. In the case of processing, the UE would firstcheck, on a received signal to see if the RNTI matches. If the RNTI doesnot match, the complement could then be taken and used to see if itmatches. If one of the RNTI or its complement matches, the UE knows thatit should use either robust or normal HARQ feedback transmissionsdepending on which RNTI matches.

Alternatively, two RNTI values could be chosen and sent to the UE. Inthis case, the matching calculations, for example XOR and CRCcalculations, are performed between the first RNTI and the receivedsignal and then the second RNTI and the received signal. If one of theRNTIs matches, the UE will know which HARQ feedback transmission to use,whether robust or normal depending on which RNTI matches.

Reference is now made to FIG. 6 a. FIG. 6 a illustrates a processdiagram for an eNB. The process starts in step 610 and proceeds to step612 in which a check is made to see whether control information needs tobe sent in a MAC-PDU header.

If yes, the process proceeds to step 614 in which the RNTI used for thetransmission of the MAC-PDU is set to the robust feedback RNTI, asdescribed above.

If, in step 612, the eNB finds that control information is not to besent in the MAC-PDU header, then the process proceeds to step 616. Instep 616, the eNB sets the RNTI to the RNTI expected for normalfeedback.

The process then proceeds from step 614 or step 616 to step 620 in whichthe MAC-PDU is transmitted using the RNTI from steps 614 or 616.

The process then proceeds to step 630 and ends.

On the UE side, reference is now made to FIG. 6 b. The process starts atstep 650 and proceeds to step 652 in which the UE receives the MAC-PDU.

The process then proceeds to step 654 in which the UE determines whetherthe RNTI associated with the MAC-PDU is for robust HARQ transmission. Ifyes, the process proceeds to step 656 in which a robust ACK or NACK isused depending on the results of the decoding process.

If no, the process proceeds from step 654 to step 660 in which a normalACK or NACK is used depending on the results of the decoding process.

The process then proceeds to step 670 and ends.

Use of a MAC Header Field

A further alternative to indicating to the UE from the eNB that a morerobust HARQ feedback transmission is required is the use of anindication within the MAC header field. As will be appreciated by thoseskilled in the art, the three methods for indication described above alluse the DLSCCH to indicate if a standard or robust configuration shouldbe used for HARQ feedback transmission. This alternative is desirable inthe case were the use of the DLSCCH is considered too costly from asystem resource point of view.

The fourth indication is therefore a new field defined in the MAC-PDUheader to indicate more repetition in transmitting an ACK from the UE toeNB. For example, the number of ACK repetitions is set to one, two ormore higher than the normal repetition configured by the RRC if theheader contains a field set to one or two.

As will be appreciated, the UE only understands if more repetition isrequired for HARQ feedback when it successfully decodes the receivedMAC-PDU. If the decoding of the MAC-PDU fails then the UE applies thenormal repetition as configured by the RRC when it sends its NACK. Thisis better illustrated with reference to FIGS. 7 a and 7 b.

FIG. 7 a illustrates the eNB behavior for setting additional repetitionwhen a MAC-PDU has control information in its header. The process startsat step 710 and in step 712 the eNB waits for a MAC-PDU to send to theUE.

Once a MAC-PDU is to be sent to the UE, the process proceeds to step 714in which a check is made to see whether or not the MAC-PDU headercontains control information. If yes, the process proceeds to step 716in which a repetition field in the MAC-PDU header is set. As indicated,the repetition field could indicate a number, such as one or two, andrepresents an increase in the number of repetitions for transmitting anACK or a NACK. Alternative configurations could use the number ofrepetitions instead of an increase indication. In another alternative asingle bit may be used to indicate that the UE should apply a predefinedincrement of repetitions. The predetermined interval may be pre-signaledto the UE from the eNB via explicit signaling; either by systembroadcast or RRC signaling.

From step 716, the process proceeds to step 720. Also, if the MAC-PDUheader does not contain any control information, the process proceedsfrom step 714 to step 720.

In step 720, the eNB reserves a feedback channel resource for therequired repetition. As will be appreciated, this needs to be setwhether or not the MAC-PDU has control information in its header.

The process then proceeds to step 722 in which the MAC-PDU istransmitted.

The process then steps to step 730 in which receives the HARQ feedbackfrom the UE and it checks whether more ACKs have been received thanNACKs or DTXs. Alternatively the eNB checks whether the number of ACKsexceeds a configured threshold. If yes, the process ends at step 740.For example, the eNB waits for 3 repetitions, and then 2 or 3 ACKs areneeded for successful transmission. Otherwise, the step retransmits theMAC-PDU in step 745 and again determines whether more ACKs are receivedthan NACKs or DTXs in step 730.

As will be appreciated by those skilled in the art, the check of step730 also checks to see whether or not the correct, or pre-determined,number of ACKs or NACKs are received. If the correct number of ACKs orNACKs are not received, then the eNB will know that either the UE didnot decode the header correctly or a DTX was received and will thus alsorequest a reserve feedback channel resource for the required repetitionin step 743 and retransmit in step 745.

From the UE perspective, reference is now made to FIG. 7 b. The processstarts in step 750 and proceeds to step 752 in which in waits for aMAC-PDU to be received.

Once a MAC-PDU is received, the process proceeds to step 754 in which itchecks to see whether decoding occurred properly.

If yes, the process then proceeds to step 760 in which it checks whetheror not a repetition field is set in the MAC-PDU header.

Depending on the results of the checks in step 754 or step 760, the ACKor NACK is repeated by a specific number of times. In particular, if thedecoding does not occur properly in step 754, then the process proceedsto step 756 in which it repeats a NACK N times. N is specified by theRRC and is typically 1.

If the repetition field is not set as found in step 760, the processproceeds to step 762 in which an acknowledgement is repeated M times.Here M is set by the RRC and is typically 1.

If the repetition field is set to a delta value as determined in step760, the process proceeds to step 764 in which the ACK is repeated Mplus delta times. As indicated above, M is set by the RRC and delta isdetermined by the repetition field in the MAC-PDU header.

From steps 756, 762 and 764 the process proceeds to step 770 and ends.

Reference is now made to Table 1 below.

TABLE 1 event probability Data Indication Failure 0.01 First ReceptionFailure 0.1 ACK->ACK 0.94 ACK->NACK 0.01 ACK->DTX 0.05 NACK->NACK 0.949NACK->ACK 0.001 NACK->DTX 0.05 DTX->DTX 0.9 DTX->ACK 0.05 DTX->NACK 0.05Success 0.891 Fail 0.099 Miss 0.01

Table 1 illustrates the probabilities of interpreting various messagesthat have been sent. In particular, as illustrated in Table 1, theprobability of an ACK being sent and an ACK being interpreted by the eNBis 94%. The probability of an ACK being sent and an NACK beinginterpreted is 1%. The probability of an ACK being sent and an DTX beinginterpreted is 5%. The table illustrates the remaining probabilities.

In the case of two repetitions, reference is now made to Table 2.

TABLE 2 Reception by 1st UE resp. 2nd UE resp. UE by eNB by eNB eNBbehaviour Probability Success ACK ACK success 0.7872876 UE sends ACKNACK retransmission 0.0083754 ACK and ACK DTX retransmission 0.041877ACK NACK ACK retransmission 0.0083754 NACK NACK retransmission 0.0000891NACK DTX retransmission 0.0004455 DTX ACK retransmission 0.041877 DTXNACK retransmission 0.0004455 DTX DTX retransmission 0.0022275 Fail NACKDTX retransmission 0.0845559 UE sends NACK ACK retransmission 0.00469755One NACK NACK NACK retransmission 0.00469755 ACK DTX retransmission0.0000891 ACK ACK success 0.00000495 ACK NACK retransmission 0.00000495DTX DTX retransmission 0.004455 DTX ACK retransmission 0.0002475 DTXNACK retransmission 0.0002475 Indication DTX DTX retransmission 0.0081missed DTX ACK retransmission 0.00045 DTX DTX NACK retransmission0.00045 ACK DTX retransmission 0.00045 ACK ACK success 0.000025 ACK NACKretransmission 0.000025 NACK DTX retransmission 0.00045 NACK ACKretransmission 0.000025 NACK NACK retransmission 0.000025

As indicated in Table 2, the UE may send an ACK, NACK or DTX. If two aresent by the UE, the probabilities of receiving two ACKs, therebyindicating success, is indicated by the various fields.

Specifically, from Table 2, success is indicated in the top line wherethe UE sends an ACK and two consecutive ACKs are received by the eNB.The probability of this is calculated by the probability of successfuldata indication*the probability of successful data reception*probabilityof ACK received as ACK*probability of ACK received asACK=(1−0.01)*(1−0.1)*(1−0.01−0.05)*(1−0.01−0.05)=78.73%.

In the remaining cases, the UE does not receive two ACKs and thereforeretransmits the MAC-PDU.

In the case of failure, the UE sends a NACK. The probability that twoACKs are interpreted by the eNB is very small, as indicated by thetable. Similarly, if the UE indicates DTX, the probability that the eNBinterprets two ACKs is also very small.

The performance of the above indicates that the success occurs 78.73% ofthe time. A detection error occurs with a probability of 0.00002995 andunnecessary retransmission occurs with the probability of 0.0502524.

The detection error probability in these cases is much smaller than thecase where the repetition is not applied. Meanwhile, overhead, such asunnecessary retransmissions, is kept quite low, assuming the frequencyof MAC-PDU with control information is 1% of the frequency of MAC-PDUswith only user payload.

The above is further improved with three repetitions. This isillustrated by Table 3.

TABLE 3 Probability 2 repetition 3 repetition Success 78.73% 88.18%Detection error 0.003% 0.033% Overhead  5.0%  0.30%

The above therefore indicates robust MAC Signaling in which a MAC-PDUwith control information in the header is sent to the eNB with anindication that robust HARQ feedback transmission should be used.

The embodiments described herein are examples of structures, systems ormethods having elements corresponding to elements of the techniques ofthis application. This written description may enable those skilled inthe art to make and use embodiments having alternative elements thatlikewise correspond to the elements of the techniques of thisapplication. The intended scope of the techniques of this applicationthus includes other structures, systems or methods that do not differfrom the techniques of this application as described herein, and furtherincludes other structures, systems or methods with insubstantialdifferences from the techniques of this application as described herein.

1. A method for indicating robust Medium Access Control (MAC) signalingcomprising the steps of: checking, at an evolved Node B (eNB), whether aMAC protocol data unit (MAC-PDU) contains control information; and ifyes, the eNB providing an indication to a user equipment (UE) to use arobust configuration for a hybrid automatic repeat request (HARQ)feedback transmission; wherein the use of the robust configuration for ahybrid automatic repeat request reduces the probability of HARQ feedbacksignal misinterpretation; and wherein the indication comprises sendingthe MAC-PDU on a reserved downlink shared control channel (DLSCCH) ifthe MAC-PDU requires robust HARQ feedback transmission and sending theMAC-PDU on a non-reserved DLSCCH if the MAC-PDU does not require robustHARQ feedback transmission.
 2. The method of claim 1, wherein a MAC-PDUindicated on a reserved DLSCCH has a different format when compared to aMAC-PDU indicated on a non-reserved DLSCCH.
 3. The method of claim 1,wherein the robust HARQ feedback transmission comprises one of:increasing transmission power for the HARQ feedback transmission;repeating acknowledgement or non-acknowledgement a pre-specified numberof times; and adding a preamble and a post-amble to the acknowledgementand non-acknowledgment messages.
 4. The method of claim 1, wherein themethod is performed on an enhanced node B.
 5. A method for interpretingan indication of robust Medium Access Control (MAC) signaling comprisingthe steps of: receiving, at a User Equipment (UE), a MAC protocol dataunit (MAC-PDU); checking whether an indication for robust hybridautomatic repeat request (HARQ) feedback transmission is provided; andif yes, utilizing, at the UE, robust hybrid automatic repeat request(HARQ) feedback transmission, wherein the use of the robust HARQfeedback transmission reduces the probability of HARQ feedback signalmisinterpretation; and wherein the indication comprises receiving theMAC-PDU on a reserved downlink shared control channel (DLSCCH) if theMAC-PDU requires robust HARQ feedback transmission and receiving theMAC-PDU on a non-reserved DLSCCH if the MAC-PDU does not require robustHARQ feedback transmission.
 6. The method of claim 5, wherein a MAC-PDUindicated on a reserved DLSCCH has a different format when compared to aMAC-PDU indicated on a non-reserved DLSCCH.
 7. The method of claim 6,wherein the format of bits is interpreted based on whether the sendingof the MAC-PDU was indicated on a reserved DLSCCH or a non-reservedDLSCCH.
 8. The method of claim 6, wherein the reserved DLSCCH is used asa default indication channel for UEs that are accessing the network inan unsynchronized manner.
 9. The method of claim 5, wherein theindication signals that a predefined increment, pre-configured by aRadio Resource Control (RRC), is used as the number by which to increasethe number of repetitions of HARQ feedback transmission.
 10. The methodof claim 5, wherein the robust HARQ feedback transmission comprises oneof: increasing transmission power for the HARQ feedback transmission;repeating acknowledgement or non-acknowledgement a pre-specified numberof times; and adding a preamble and a post-amble to acknowledgement andnon-acknowledgment messages.
 11. The method of claim 5 wherein therobust configuration for HARQ feedback transmission is signaled by aRadio Resource Control signaling during radio bearer configuration orre-configuration.
 12. An enhanced Node B (eNB) adapted configured toindicate robust Medium Access Control (MAC) signaling, characterized by:a checking module to check whether a MAC protocol data unit (MAC-PDU)contains control information; and a providing module to provide anindication to use a robust configuration for a hybrid automatic repeatrequest (HARQ) feedback transmission; wherein the use of the robustconfiguration for a hybrid automatic repeat request reduces theprobability of HARQ feedback signal misinterpretation; wherein theindication comprises one of: a) sending the MAC-PDU on a reserveddownlink shared control channel (DLSCCH) if the MAC-PDU requires robustHARQ feedback transmission and sending the MAC-PDU on a non-reservedDLSCCH if the MAC-PDU does not require robust HARQ feedbacktransmission; and b) a different Radio Network Temporary Identity (RNTI)for MAC-PDUs requiring robust HARQ feedback transmission than the RNTIfor MAC-PDUs not requiring robust HARQ feedback transmission.
 13. TheeNB of claim 12, wherein the checking module further checks the HARQfeedback received and compares the number of feedback messages expectedaccording to the associated robust HARQ indicator of the originallytransmitted MAC-PDU.
 14. A User Equipment (UE) configured to interpretan indication of robust Medium Access Control (MAC) signaling,characterized by: a receiving module for receiving a MAC protocol dataunit (MAC-PDU); a checking module for checking whether an indication forrobust hybrid automatic repeat request (HARQ) feedback transmission isprovided; and a utilizing module for utilizing robust hybrid automaticrepeat request (HARQ) feedback transmission; wherein the use of therobust HARQ feedback transmission reduces the probability of HARQfeedback signal misinterpretation; and wherein the indication comprisesone of: a) receiving the MAC-PDU on a reserved downlink shared controlchannel (DLSCCH) if the MAC-PDU requires robust HARQ feedbacktransmission and receiving the MAC-PDU on a non-reserved DLSCCH if theMAC-PDU does not require robust HARQ feedback transmission; and b) adifferent Radio Network Temporary Identity (RNTI) for MAC-PDUs requiringrobust HARQ feedback transmission than the RNTI for MAC-PDUs notrequiring robust HARQ feedback transmission.
 15. A method for indicatingrobust Medium Access Control (MAC) signaling comprising the steps of:checking, at an evolved Node B (eNB), whether a MAC protocol data unit(MAC-PDU) contains control information; and if yes, the eNB providing anindication to a user equipment (UE) to use a robust configuration for ahybrid automatic repeat request (HARQ) feedback transmission; whereinthe use of the robust configuration for a hybrid automatic repeatrequest reduces the probability of HARQ feedback signalmisinterpretation; and wherein the indication comprises the use of adifferent Radio Network Temporary Identity (RNTI) for MAC-PDUs requiringrobust HARQ feedback transmission from the RNTI for MAC-PDUs notrequiring robust HARQ feedback transmission.
 16. The method of claim 15,wherein two RNTIs are signaled to a User Equipment (UE) utilizing aRadio Resource Control (RRC) message.
 17. The method of claim 15,wherein one RNTI is signaled to a User Equipment (UE) utilizing a RadioResource Control signaling and the UE takes a complement of the RNTI touse to determine the alternative RNTI.
 18. A method for interpreting anindication of robust Medium Access Control (MAC) signaling comprisingthe steps: receiving, at a User Equipment (UE), a MAC protocol data unit(MAC-PDU); checking whether an indication for robust hybrid automaticrepeat request (HARQ) feedback transmission is provided; and if yes,utilizing, at the UE, robust hybrid automatic repeat request (HARQ)feedback transmission, wherein the use of the robust HARQ feedbacktransmission reduces the probability of HARQ feedback signalmisinterpretation; and wherein the indication comprises the use of adifferent Radio Network Temporary Identity (RNTI) for MAC-PDUs requiringrobust HARQ feedback transmission from the RNTI for MAC-PDUs notrequiring robust HARQ feedback transmission.
 19. The method of claim 18,wherein two RNTIs are signaled to the User Equipment (UE) utilizing aRadio Resource Control (RRC).
 20. The method of claim 19, wherein oneRNTI is signaled to the User Equipment (UE) utilizing a Radio ResourceControl signaling and the UE takes a complement of the RNTI to use indetermining the alternative RNTI.